As described in the following document, it is recommended to consider the routing delay in the package when the frequency exceeds (or exceeds) a certain level depending on each device and memory protocol.
(Reference) External Memory Interface Handbook Volume 2: Design Guidelines
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/ literature/hb/external-memory/emi_plan.pdf
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Package Deskew Recommendation for Stratix V Devices
(e.g. Stratix V, DDR3 above 800MHz)
Package Deskew Recommendations for Arria 10 and Stratix 10 Devices
For Arria 10 and Stratix 10 with DDR4/DDR3, it is recommended to operate at the following frequency or higher.
Single Rank : 933[MHz]
Dual Rank : 800[MHz]
Quard Rank : 667[MHz]
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Category: External Memory Interface
Tools: -
Devices: Stratix® 10 / Stratix® V / Arria® 10